Post-treatment residual tissue in idiopathic retroperitoneal fibrosis: active residual disease or silent "scar" ? A study using 18F-fluorodeoxyglucose positron emission tomography.

OBJECTIVE

Medical treatment is often effective in idiopathic retroperitoneal fibrosis (IRF) but frequently leads to residual retroperitoneal masses that may represent active disease or simply consist of inactive fibrotic tissue. 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) is a functional imaging modality that reliably assesses disease activity in a number of inflammatory diseases including IRF. We used 18F-FDG PET to evaluate the metabolic activity of residual masses in a series of IRF patients.

METHODS

We studied 7 consecutive IRF patients, all of whom presented constitutional symptoms and/or pain, and had high acute-phase reactant levels; 6 had ureteral involvement. IRF was diagnosed by means of computed tomography (CT), which revealed a peri-aortoiliac mass in all cases. Three patients underwent surgical ureterolysis and 2 received ureteral stents. Subsequently, 5 patients received prednisone, one sequential treatment with prednisone and tamoxifen, and one prednisolone plus methotrexate. All of the patients underwent 18F-FDG PET at varying times after the end of treatment.

RESULTS

The presenting signs/symptoms improved in all patients and the levels of acute-phase reactants significantly decreased or normalised. Ureteral obstructive disease resolved in all cases. Post-treatment CT revealed a considerable reduction in the amount of IRF but all of the patients had a residual retroperitoneal mass. PET revealed slight aorto-iliac 18F-FDG uptake in only one patient; all of the others were negative. No patient relapsed during the follow-up.

CONCLUSIONS

Post-treatment residual masses are frequent in IRF patients but, in most cases, probably represent metabolically inactive tissue.